Investment Securities (Investment) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Investment [Line Items]
Investments	$ 46,500	$ 43,662
Domestic Corporate Debt Securities [Member]
Investment [Line Items]
Debt and AFS securities, Amortized cost	19,800	19,600
Debt securities, Gross unrealized gains	3,510	2,323
Debt securities, Gross unrealized losses	(91)	(217)
Domestic Corporate Debt Securities [Member] | Estimated Fair Value [Member]
Investment [Line Items]
Debt securities, Estimated fair value	23,219	21,706
US States and Political Subdivisions Debt Securities [Member]
Investment [Line Items]
Debt and AFS securities, Amortized cost	5,144	4,245
Debt securities, Gross unrealized gains	497	235
Debt securities, Gross unrealized losses	(96)	(191)
US States and Political Subdivisions Debt Securities [Member] | Estimated Fair Value [Member]
Investment [Line Items]
Debt securities, Estimated fair value	5,545	4,289
Commercial Mortgage Backed Securities [Member]
Investment [Line Items]
Debt and AFS securities, Amortized cost	2,933	2,929
Debt securities, Gross unrealized gains	207	188
Debt securities, Gross unrealized losses	(42)	(82)
Commercial Mortgage Backed Securities [Member] | Estimated Fair Value [Member]
Investment [Line Items]
Debt securities, Estimated fair value	3,098	3,035
Residential Mortgage Backed Securities [Member]
Investment [Line Items]
Debt and AFS securities, Amortized cost	1,755	1,819
Debt securities, Gross unrealized gains	153	139
Debt securities, Gross unrealized losses	(30)	(48)
Residential Mortgage Backed Securities [Member] | Estimated Fair Value [Member]
Investment [Line Items]
Debt securities, Estimated fair value	1,878	1,910
Asset-backed Securities [Member]
Investment [Line Items]
Debt and AFS securities, Amortized cost	7,685	7,373
Debt securities, Gross unrealized gains	33	60
Debt securities, Gross unrealized losses	(36)	(46)
Asset-backed Securities [Member] | Estimated Fair Value [Member]
Investment [Line Items]
Debt securities, Estimated fair value	7,682	7,387
Foreign Corporate Debt Securities [Member]
Investment [Line Items]
Debt and AFS securities, Amortized cost	1,666	1,741
Debt securities, Gross unrealized gains	179	103
Debt securities, Gross unrealized losses	(50)	(86)
Foreign Corporate Debt Securities [Member] | Estimated Fair Value [Member]
Investment [Line Items]
Debt securities, Estimated fair value	1,795	1,758
Foreign Government Debt Securities [Member]
Investment [Line Items]
Debt and AFS securities, Amortized cost	2,011	2,336
Debt securities, Gross unrealized gains	118	81
Debt securities, Gross unrealized losses	(3)	(7)
Foreign Government Debt Securities [Member] | Estimated Fair Value [Member]
Investment [Line Items]
Debt securities, Estimated fair value	2,126	2,410
US Treasury and Government [Member]
Investment [Line Items]
Debt and AFS securities, Amortized cost	698	752
Debt securities, Gross unrealized gains	50	45
Debt securities, Gross unrealized losses	(1)	(27)
US Treasury and Government [Member] | Estimated Fair Value [Member]
Investment [Line Items]
Debt securities, Estimated fair value	747	770
Retained Interest [Member]
Investment [Line Items]
Retained interests and AFS securities, Amortized cost	60	64
Retained interests, Gross unrealized gain	13	8
Retained interests, Gross unrealized loss	0	0
Retained Interest [Member] | Estimated Fair Value [Member]
Investment [Line Items]
Retained interests, Estimated fair value	73	72
Available-for-sale Securities [Member]
Investment [Line Items]
Debt and AFS securities, Amortized cost	215	203
Retained interests, Gross unrealized gain	71	51
Available-for-sale Equity Securities, Gross Unrealized Loss	(2)	(3)
Available-for-sale securities, Equity, Estimated fair value	284
Available-for-sale Securities [Member] | Estimated Fair Value [Member]
Investment [Line Items]
Available-for-sale securities, Equity, Estimated fair value		251
Trading Securities [Member]
Investment [Line Items]
Trading Securities, Unrealized Holding Gain	0	0
Trading Securities, Unrealized Holding Loss	0	0
Trading Securities [Member] | Amortized Cost [Member]
Investment [Line Items]
Trading Securities	53	74
Trading Securities [Member] | Estimated Fair Value [Member]
Investment [Line Items]
Trading Securities	53	74
Total [Member]
Investment [Line Items]
Retained interests, Gross unrealized gain	4,831	3,233
Retained interests, Gross unrealized loss	(351)	(707)
Total [Member] | Amortized Cost [Member]
Investment [Line Items]
Marketable Securities	42,020	41,136
Total [Member] | Estimated Fair Value [Member]
Investment [Line Items]
Marketable Securities	46,500
Investments		43,662
Mortgage-backed Securities, Issued by Private Enterprises [Member] | Residential Mortgage Backed Securities [Member]
Investment [Line Items]
Debt securities, Estimated fair value	640
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Residential Mortgage Backed Securities [Member]
Investment [Line Items]
Debt securities, Estimated fair value	$ 1,238